1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device having a circuit comprising a thin film transistor (hereinafter referred to as a TFT), for example, an electro-optical device represented by a liquid crystal display panel and an electronic device in which such an electro-optical device is mounted as parts.
Note that in this specification, a semiconductor device indicates a general device functioning by utilizing semiconductor characteristics, that is, an electro-optical device, a semiconductor device, and an electronic device each are a semiconductor device.
2. Description of the Related Art
In recent years, a technique of structuring a thin film transistor (TFT) using a semiconductor thin film (about several to several hundred nm in thickness) formed on a substrate having an insulating surface is drawing attention. The thin film transistor is widely applied to an electronic device such as an IC or an electro-optical device. In particular, the development for a switching element of an image display device is being advanced.
A material of a crystalline semiconductor film suitably used for the TFT is silicon. A silicon film having a crystalline structure (hereinafter referred to as a crystalline silicon film) is generally formed through the following process. That is, an amorphous silicon film is deposited on a substrate made of glass. quartz. or the like by a plasma CVD method or a low pressure CVD method and then crystallized by heating treatment or laser light irradiation (hereinafter referred to as laser processing in this specification) to obtain the crystalline silicon film.
However, in the case of the crystalline silicon film produced by the above conventional method. the crystal orientation planes are present randomly and an orientation ratio with respect to a specific crystal orientation is low. When the orientation ratio is low, it is almost impossible to keep continuity of lattices because of a grain boundary produced by collision of crystals with different orientations. Thus, it can be estimated that a large number of dangling bonds are produced. Dangling bonds which can be produced in the grain boundary become trapping centers of carriers (electron and hole) to reduce transporting characteristics. That is, since the carriers are scattered or trapped, even when a TFT is manufactured using such a crystalline semiconductor film, a TFT having high field effect mobility cannot be expected.
Also, a large number of distortions, defects and the like are present in a silicon film having a crystalline structure, that is, in a polysilicon film. They function as traps of carriers to deteriorate electrical characteristics. Thus, even in the channel forming region of the TFT, an existence configuration of a distortion, a volume of a lattice defect, and the like become large factors for causing a variation in characteristic.
An object of the present invention is to provide means for solving such problems. That is, an object of the present invention is to increase an orientation ratio of a crystalline semiconductor film obtained by crystallizing an amorphous semiconductor film and to suppress a distortion thereof so that a TFT using such a crystalline semiconductor film is provided.
The present invention is characterized in that at the time of formation of the amorphous semiconductor film or after the formation thereof, a noble gas, typically, argon is included in the semiconductor film and crystallization is performed therefor, and thus an orientation ratio of the film can be increased and a distortion present in the semiconductor film after the crystallization is suppressed as compared with that present in the semiconductor film before the crystallization.
Also, the crystallization of the present invention is characterized in that a metallic element for promoting crystallization of silicon is introduced, a crystalline silicon film is formed by heating treatment at a lower temperature than a conventional one, and a noble gas element is removed or reduced by laser light irradiation performed later.
A distribution of crystal orientation is preferably obtained from an electron backscatter diffraction pattern (EBSP). In the case of the EBSP method, a dedicated purpose detector is provided in a scanning electron microscopy (SEM) and a crystal orientation is analyzed from back scattering of a primary electron. When an electron beam is incident into a sample having a crystalline structure, inelastic scattering is also caused in the rear. Of the inelastic scattering, a linear pattern inherent to a crystal orientation due to Bragg diffraction in the sample (generally called a Kikuchi pattern) is also observed. In the case of EBSP, a Kikuchi pattern displayed on the screen of the detector is analyzed to obtain a crystal orientation of the sample. When an orientation analysis is repeated while a position of the sample into which an electron beam is irradiated is shifted (a mapping measurement is performed), information of crystal orientation or alignment can be obtained with respect to a sheet sample. When all crystal orientations of respective crystal grains are obtained by the mapping measurement, a state of crystal orientations in a film can be statistically displayed.
The present inventor(s) et al. performed the following experiment.
(Experiment)
First, a sample in which a base insulating film (silicon oxynitride film: 150 nm in thickness) is formed on a glass substrate and an amorphous silicon film having a thickness of 54 nm is formed thereon by a plasma CVD method is prepared. Next. argon is added to the amorphous silicon film by an ion doping method. An ion doping condition at this time is set such that an accelerating voltage is 30 kV, a dose is 2xc3x971015/cm2, and a concentration of argon included in the film is about 3xc3x971020/cm3. Next, a solution including nickel at 100 ppm in weight conversion is applied to the amorphous silicon film and then thermal treatment is performed at 500xc2x0 C. for 1 hour. After that, thermal treatment is performed at 600xc2x0 C. for 8 hours to crystallize the amorphous silicon film. Thus, a silicon film having a crystalline structure is formed. A distribution of crystal orientation in the thus obtained silicon film having the crystalline structure is examined by an EBSP.
FIG. 14 is an inverse pole figure obtained from the EBSP. The inverse pole figure is often used in the case where a preferred orientation of polycrystal is displayed and collectively indicates which lattice plane is coincided with a specific surface (here, the surface of the film) of the sample. Note that an object having a fan shape in FIG. 14 is generally called a standard triangle and all indexes with respect to a cubic system are included therein. Also, a length in this drawing corresponds to an angle with respect to a crystal orientation. For example, an angle between {001} and {101} is 45 degrees, an angle between {101} and {111} is 35.26 degrees. and an angle between {111} and {001} is 54.74 degrees.
Also, FIG. 14 is obtained by plotting all measurement points by mapping on the standard triangle. Since a density of points becomes high near {101} and {111}, it can be read that a preferred orientation is made for specific indexes (here, {111} and {111}.
Thus, when it is clear that a preferred orientation is made for specific indexes, a ratio as to what degree of crystal grains is gathered near the indexes is digitized and thus the degree of the preferred orientation is easy to image. In the inverse pole figure as shown in FIG. 14, a ratio of the number of points present within an area produced by a deviation angle of 10 degrees from {111} to the whole can be indicated as an orientation ratio.
With respect to the thus obtained orientation ratio, a ratio in the case where an angle produced by a {101} plane detected by a reflection electron diffraction pattern method and the surface of the silicon film is within 10 degrees is 16%. a ratio in the case where an angle produced by a {111} plane and the surface of the semiconductor film is within 10 degrees is 14%, and a ratio in the case where an angle produced by a {001} plane and the surface of the semiconductor film is within 10 degrees is 1%. That is, as compared with the {001} plane, the orientation ratio of crystal becomes higher in the {101} plane and the {111} plane.
Also, information with respect to a distortion is preferably obtained by an X-ray diffraction method. According to the X-ray diffraction method, a diffraction strength is measured while scanning a diffraction angle 2xcex8. At this time, an interval xe2x80x9cdxe2x80x9d between lattice planes in the Bragg equation (2d sin xcex8=xcex. where xcex is a wavelength of an X-ray) can be obtained from a measurement of 2xcex8 when the strength becomes a peak. Here, when a 2xcex8 scanning is delayed to determine a peak position with precision, information with respect to a distortion applied to a lattice can be also obtained.
According to a structure disclosed in this specification, there is provided a method of manufacturing a semiconductor device, including: a first step of forming a first semiconductor film having an amorphous structure on an insulating surface. a second step of adding a noble gas element to the first semiconductor film having the amorphous structure; a third step of adding a metallic element to the first semiconductor film having the amorphous structure; a fourth step of heating the first semiconductor film and then irradiating laser light thereto for crystallization to form a first semiconductor film having a crystalline structure: a fifth step of forming a barrier layer on a surface of the first semiconductor film having the crystalline structure; a sixth step of forming a second semiconductor film including a noble gas element on the barrier layer; a seventh step of gettering the metallic element to the second semiconductor film to remove or reduce the metallic element in the first semiconductor film having the crystalline structure; and an eighth step of removing the second semiconductor film.
In the above structure, a method of manufacturing a semiconductor device is characterized in that the fifth step of forming the barrier layer is a step of oxidizing the surface of the first semiconductor film having the crystalline structure by laser light irradiation and then oxidizing the surface of the first semiconductor film having the crystalline structure by a solution including ozone.
Also, in the above structure, a method of manufacturing a semiconductor device is characterized in that in the second step, the noble gas element is added to the first semiconductor film having the amorphous structure at a concentration of 1xc3x971017/cm3 or higher, preferably. in a concentration range of 1xc3x971020/cm3 to 3xc3x971020/cm3.
Also, in the above structure, a method of manufacturing a semiconductor device is characterized in that the noble gas element included in the first semiconductor film is removed or reduced by the laser light irradiation in the fourth step.
Also, according to another structure of the present invention, there is provided a method of manufacturing a semiconductor device, including: a first step of forming a first semiconductor film having an amorphous structure on an insulating surface: a second step of adding a noble gas element to the first semiconductor film having the amorphous structure; a third step of adding a metallic element to the first semiconductor film having the amorphous structure; a fourth step of heating the first semiconductor film and then irradiating laser light thereto for crystallization to form a first semiconductor film having a crystalline structure; a fifth step of selectively adding a noble gas element to the first semiconductor film having the crystalline structure to form a region including the noble gas element; a sixth step of gettering the metallic element to the region including the noble gas element to selectively remove or reduce the metallic element in the first semiconductor film having the crystalline structure; and a seventh step of removing the region including the noble gas element.
Also, in the above structure, a method of manufacturing a semiconductor device is characterized in that in the second step, the noble gas element is added to the first semiconductor film having the amorphous structure at a concentration of 1xc3x971017/cm3 or higher, preferably, in a concentration range of 1xc3x971020/cm3 to 3xc3x971020/cm3.
Also, in the above structure, a method of manufacturing a semiconductor device is characterized in that the noble gas element included in the first semiconductor film is removed or reduced by the laser light irradiation in the fourth step.
Also, in the respective structures described above, a method of manufacturing a semiconductor device is characterized in that the second semiconductor film is formed by a sputtering method using a semiconductor as a target in an atmosphere containing the noble gas element. Also, in the method of manufacturing a semiconductor device, the second semiconductor film is formed by a sputtering method using a semiconductor including one of phosphorus and boron as a target in an atmosphere containing the noble gas element. Also, in the respective structures described above, the second semiconductor film may be formed by a PCVD method in which film formation is performed in the atmosphere containing the noble gas element.
Also, in the respective structures described above, a method of manufacturing a semiconductor device is characterized in that the sixth step is heating treatment or processing for irradiating intense light to the semiconductor film. Also, the sixth step may be processing for performing heating and irradiating intense light to the semiconductor film.
Also, in the respective structures described above, a method of manufacturing a semiconductor device is characterized in that the intense light is light emitted from one selected from the group consisting of a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, and a high pressure mercury lamp.
Also, in the respective structures described above, it is preferable that in the sixth step, the concentration of the noble gas element contained in the second semiconductor film is higher than that contained in the first semiconductor film having a crystal structure.
Also, after forming a semiconductor film having an amorphous structure. the semiconductor film may be crystallized by using a metal element which promotes crystallization, and according to still another structure of the present invention, a method of manufacturing a semiconductor device is characterized by including: a first step of forming a semiconductor film which includes a noble gas element and has an amorphous structure on an insulating surface; a second step of adding a metallic element to the semiconductor film having the amorphous structure; and a third step of heating the first semiconductor film and then irradiating laser light thereto for crystallization to form a semiconductor film having a crystalline structure.
After forming a semiconductor film having an amorphous structure by allowing the film to include a noble gas element at the time of film formation, the semiconductor film may be crystalized by using elements which promote crystallization and gettering may be made thereto, according to another structure of the present invention, there is provided a method of manufacturing a semiconductor device, including: a first step of forming on an insulating surface a first semiconductor film which includes a noble gas element and has an amorphous structure; a second step of adding a metallic element to the first semiconductor film having the amorphous structure; a third step of heating the first semiconductor film and then irradiating laser light thereto for crystallization to form a first semiconductor film having a crystalline structure; a fourth step of forming a barrier layer on a surface of the first semiconductor film having the crystalline structure: a fifth step of forming a second semiconductor film including a noble gas element on the barrier layer; a sixth step of gettering the metallic element to the second semiconductor film to remove or reduce the metallic element in the first semiconductor film having the crystalline structure; and a seventh step of removing the second semiconductor film.
Also, in the above structure, the second semiconductor film may be formed by a sputtering method using a semiconductor as a target in an atmosphere containing the noble gas element or by a PCVD method in which film formation is performed in the atmosphere containing the noble gas element. Also, the second semiconductor film may be formed by a sputtering method using a semiconductor including one of phosphorus and boron as a target in an atmosphere containing the noble gas element.
Also, in the above structure, it is preferable that, when the second semiconductor film is formed, the concentration of the noble gas element contained in the second semiconductor film is higher than that of the first semiconductor film having the crystalline structure.
Also, in the respective structures described above, a method of manufacturing a semiconductor device is characterized in that the metallic element is at least one selected from the group consisting of Fe, Ni, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au.
Also, in the respective structures described above, a method of manufacturing a semiconductor device is characterized in that the noble gas element is at least one selected from the group consisting of He, Ne, Ar, Kr, and Xe.